It is only on this supposition that we can explain how the horizon of vision grows wider and wider the higher the position we choose, how the tops of towers and mountains at a distance become visible before the bases, how the hull of a ship disappears first as she sails away, and how, as we go from the poles towards the equator, new stars become visible. Besides these proofs, there are many others, such as the circular shadow of the earth seen on the moon during an eclipse, the gradual appearance and disappearance of the sun, and especially the fact that since 1519 the earth has been regularly circumnavigated. The earth is not, however, an exact sphere, but is very slightly flattened at the poles, so as to have the form known as an oblate spheroid. In this way the polar diameter, or diameter from pole to pole, is shorter than the diameter at right angles to this--the equatorial diameter. The most accurate measurements make the polar diameter about twenty-seven miles less than the equatorial, the equatorial diameter being found to be 7,925.6 miles, and the polar 7,899.14. What were “Ducking Stools”? A ducking stool was a sort of a chair in which “common scolds” were formerly tied and plunged into water. They were of different forms, but that most commonly in use consisted of an upright post and a transverse movable beam on which the seat was fitted or from which it was suspended by a chain. The ducking stool is mentioned in the Doomsday survey; it was extensively in use throughout the country from the fifteenth till the beginning of the eighteenth century, and in one rare case at least--at Leominster--was used as lately as 1809. The Story in Photo-Engraving[30] Modern advertising would not have been possible without photo-engraving. Attention has been attracted, desire has been created and goods have been sold, largely through the pictorial or other artistic embellishments which have lifted particular “ads” out of the mass and attracted the favorable attention of the cursory reader. Pictures are the universal language, not only to those of divers tongues, but to those of every stage of mental development. Photo-engravings are a comparatively modern product. They superseded wood engravings, which for years has been the recognized medium for illustrations to print on a type printing press. Photo-engravings, broadly speaking, are divided into two classes--line engravings and halftones. The distinction between them lying in the fact that one, as its name implies, is a reproduction of a drawing made in lines or stipples, while the other, the halftone, gets its name from the method of its manufacture.